This invention relates to detonation sensors for use in systems to detect knock or detonation in internal combustion engines. It particularly relates to such sensors of the magnetostrictive type in which a magnetostrictive element serving as a flux path for a source of constant magnetic flux is surrounded by a pickup coil wound on a spool and subjected to engine vibrations to vary the flux therein and generate corresponding signals in the pickup coil.
The engine knock or detonation to be detected by such a sensor has been found to produce vibrations in the engine which show a particular characteristic relationship between amplitude and frequency, at least for a particular type of engine. This relationship usually takes the form of strong vibrations due to knock at at least one particular characteristic frequency. Since there are usually many other sources of vibration in a typical internal combustion engine, it is desirable to distinguish those vibrations due to knock from the other vibrations if knock is to be accurately detected. In this regard, it is often helpful to provide a sensor with a predetermined frequency response characteristic to attenuate in its output signal those vibrations at other frequencies compared with those vibrations at the characteristic frequency due to knock.
This invention further relates to detonation sensors of the type designed for use on actual working engines in motor vehicles and therefore designed for mass production at a reasonable cost. Such sensors are useful in systems which detect knock and control engine spark timing to maintain said knock at a level which is acceptable to a vehicle operator. The materials and assembly techniques used in the manufacture of such sensors help determine their suitability for such mass use as opposed to manufacture and use in much smaller volume as more expensive laboratory test equipment.